The increasing energy demands of industrialized and developing nations combined with the increased concern for environmental effects of fossil fuel use have placed a greater emphasis and need on developing clean and efficient alternative energy sources. If properly harnessed, the tidal flows of oceans and rivers, as well as the force of the wind, can efficiently generate vast amounts of clean energy.
The prior art discloses many devices for harnessing the energy of flowing fluids, such as the current in a river or stream, the tidal flow of an ocean, or simply the force of the wind. For example, Williamson U.S. Pat. No. 4,203,702 discloses a water driven engine wherein a diverter diverts the flow of water onto the outer blades of two counter-rotating turbines mounted in side-by-side relation, thereby producing contradirectional rotation of the turbines to generate power. Williamson U.S. Pat. No. 4,174,923 shows a similar wind driven engine.
Straumsnes U.S. Pat. No. 3,928,771, discloses a water driven engine wherein flowing water is directed by a venturi shaped inlet in the engine housing through a passageway formed between two counter-rotating turbines. Haberer U.S. Pat. No. 4,075,545 similarly discloses a wind driven engine for charging a car battery which incorporates a venturi shaped inlet to force air through the passageway maintained between two counter-rotating rotors.
The venturi shaped inlets, as shown in the prior art, are used to concentrate and increase the velocity of fluid flow between the rotors, thereby increasing the fluid flow engine power and efficiency. In many applications it would be desirable to be able to vary the fluid velocity to vary the engine power based on power demands. Although the prior art discloses means for increasing fluid flow engine power, means for varying the engine power by varying the fluid velocity are not disclosed.